Recent work by Slutsky et al., 1985 has shown that the yeast, Candida albicans has the ability to switch frequently exhibiting a number of different phenotypes which can be distinguished by their general colony morphology. This ability to switch may give an added advantage to C. albicans in its pathogenicity and also render it resistant to several common antifungal agents. This study will examine the ability of oral commensal strains of C. albicans to switch at the site of an oral candidiasis infection in immunocompromised patients. The oral isolates will be cloned and the predominant strain and switch frequency will be determined. EcoR1 digests of DNA from different phenotypes and DNA probes of moderately repetitive elements will be used in a comparison to establish strain differences. Sugar assimilation patterns will also be used as a means of identifying the different phenotypes. Developmental behavior of the different phenotypes will be explored under standard laboratory conditions and their sensitivity to antifungal agents established. These experiments should identify changes which may have occured to alter the pathogenicity of Candida albicans when switching between phenotypes. Ultimately, it is hoped that if the switching does increase the pathogenicity of this organism then it may be possible to turn the "switch off" and ensure that the organism remains sensitive to the antifungal agent.